package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

/**
 * @author: liufh
 * @create: 2021-06-27 23:47
 **/
public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {
        Executor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>)list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> list = selectList(statementid, params);
        if (list.size() == 1) {
            return (T)list.get(0);
        } else {
            throw new RuntimeException("查无结果或者查询结果过多");
        }
    }

    @Override
    public int insert(String statementid, Object param) throws Exception {
        return update(statementid, param);
    }

    @Override
    public int update(String statementid, Object param) throws Exception {
        Executor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        int count = simpleExecutor.update(configuration, mappedStatement, param);

        return count;
    }

    @Override
    public int delete(String statementid, Object param) throws Exception {
        return update(statementid, param);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        //使用JDK动态代理来为Dao接口生成代理对象，并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //底层都还是去执行JDBC代码（根据不同情况，调用selectList/selectOne或者insert/update/delete）
                //准备参数1.statementId:sql语句唯一标识：namespace.id=接口全限定名.方法名
                String className = method.getDeclaringClass().getName();
                String methodName = method.getName();
                String statementId = className + "." + methodName;
                MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
                String sqlType = mappedStatement.getType();
                //准备参数2.params:args
                //获取被调用方法的返回值类型
                Type genericReturnType = method.getGenericReturnType();
                switch (sqlType) {
                    case "INSERT": return insert(statementId, args[0]);
                    case "UPDATE": return update(statementId, args[0]);
                    case "DELETE": return delete(statementId, args[0]);
                    default:
                        //判断是否进行了 泛型类型参数化
                        if (genericReturnType instanceof ParameterizedType) {
                            return selectList(statementId, args);
                        }
                        return selectOne(statementId, args);
                }
            }
        });

        return (T)proxyInstance;
    }

}
